Pilot device for rotary tools



May 9, 1950 J. B. GIERN ET AL PILOT DEVICE FOR ROTARY TOOLS Filed NOV. l'7, 1948 Patented May 9, 1950 UNITED STATES PATENT OFFICE James B. Giern, Romeo, and Anders 1?. Anholtt, Detroit, Mich;

Application November 1'1, 1948, Serial No. 60,464

the. bushing holder is held stationary, thereby eliminating, friction and wear between the bushing and. the tool and consequently eliminating the heat resulting from such friction.

Another obj eat is to provide a pilot device of the foregoing character, wherein the tool and rotary bushing can be fitted so snugly to each other that wobble, and consequently inaccuracy, of the ro tary tool is greatly reduced.-

Another object is to provide a pilot device of the foregoing character wherein the rotary bushing and the bushing holder directly constitutes the inner and outer races of the bearing elements, thereby eliminating the need for separate bearing races and. consequently reducing the over all diameter of the device for a given size of tool.

Another object is to provide a. pilot device of the foregoing. character, wherein the bearingv elements are widely spaced axially along the bushing, thereby still further reducing any tendency of the bushing to wobble within the bushing holder the bushing rotates with the tool.v

A still further object is to provide a pilot; device: of the foregoing character so constructed and arranged that both radial and axial thrusts are counteracted and substantially eliminated, there by reducing wear.

In the drawings:

Figure l is a vertical longitudinal section of the pilot device, according to a preferred form of the invention;

Figure 2 is a top plan view of the pilot device shown in Figure 1;

Figure 3 is a side elevational view thereof; and

Figure 4 is a cross section taken along the line i in Figure 1.

Referring to the drawings in detail, Figure 1 shows a preferred form of this invention, generally designated ill. The pilot device I consists generally of a hardened rotary bushing H, rotatably mounted within a stationary bushing holder l2 by means of bearing elements l3 and I4, preferably consisting of ball bearings, housed in annular cavities t5 and I 6 respectively: The" upper wall of the annular cavity I5 is formed by providing the bushing H with a stepped portion formed an annular'shoulder l1 lying between;v the annular: portion 3 and the": reduced diameter portion r9 Above the annular portion I 8 the bushing H is provid'edwith an annular flange spaced slightly away from the upper end 2| of the. bushing. holder- E2? to establish a clearance thereb'etween;

The bushing H isiprovided' with a: longitudinal bore 22 of. such a. diameter as will snugly fit the rotary teoltdbe guided-and: yet, atthe same time,

permit the tool to be; fed longitudinally through the. bore 22 into the: workpiece (not shown). The upper end. of the bore: 22 isrounded as at 23 to facilitate the insertion-of a tool. The lower end portion of. the bushing, i2 is threaded as at 24 to receive? a correspondingly threaded retaining nut or collar 25 having a lower end flange 26 and an upper end 21.

The upper end: portion of the bushing holder in is providedwith acounterbore- 28 for receiving the.- annular portion I 8 of the bushing ll. The- 25 annular bottom wall: 29 of thecounterbore 28 serves aethe lower wa-llof the cavity I5 and leads,

to a reduced diametenbore 30',- which receives-the reduced diameter portion l9 of the bushing It.

The lower end portion-of the bushing holder i2 is also provided with a counterbore- 3 l for receiving,

the upper end 211-. oi the retaining nut" 25.v The annular top wall 32 of the counterbore 31 serves as theupper. wall of the cavity 16, Forming the bottom wallot the cavity is; and supporting: the bearing element M- therein is a. wear or thrust ring, 33,, preferably oi steel, which is; in turn,- supported by' the upper end 21 of retaining nutl 25.. Thrust ring 33'notonly helps to: compensate for inaccuracies incounterborestt' and 3-1, but

also absorbs any frictional tendency of bearing element M, in the course of operation, to unscrew threaded retaining nut 25 from its engagement with threaded lower end portion 24 of bushing l2. Annular flange 26 of nut 25 is spaced slightly away from the lower end of the bushing holder l2 to establish a clearance therebetween, thus preventing friction which might also tend to unscrew the retaining nut 25.

In order to prevent dirt from entering the bearing elements I3 and M, as well as to prevent leakage of lubricant, the bearing holder I2 is provided with axially-spaced annular recesses 34, 35 and 36 containing oil retaining rings 31 of rubber, felt, or any suitable material. Extending radially thru one side of the bushing holder I2 is an oil hole 38 by means of which lubricant may be furnished to the bearing elements l3 and 4. The upper end portion 2| of the bushing holder I2 is provided with a flange 39 to prevent the bushing holder from slipping down into the die (not shown). Into the outer edge of the flange 39 is cut a notch or similar aperture 40 into which a stationary dog (not shown), part of the die, may be inserted to prevent rotation of the bushing holder.

In the operation of the invention, let it be assumed that the pilot device ID has been inserted in a hole in the jig so that the dog (not shown), which projects upward and inward near the edge of the hole, engages the notch 40 in the flange 39 of the bushing holder 12. The rotary tool, such as a drill, is then inserted in the bore 22 in the rotary bushing H so that it fits snugly and will cause the bushing to turn with it. The operator now operates the machine in the usual manner causing the tool to be fed downward through the bushing bore 22 into the workpiece. The relatively snug fit between the tool and the bushing bore 22 prevents the tool from wobbling and insures an accurately located bore which is also of accurate diameter. The tool causes the bushing 22 to rotate upon its anti-friction bearing assemblies l3 and I4, transferring the radial thrust through these to the shouldered bushing holder l2 and the axial thrust to the thrust ring 33 mounted on the bearing retainer.

By the use of the present invention, the bearing bushing and bushing holders serve directly as the bearing raceways, and therefore enable the over all diameter of the bushing holder to be of the minimum diameter. The members H and I2 are also conveniently manufactured by automatic machinery and the annular shoulders thereon may be ground easily and efficiently. It is preferable that a clearance of about 20 thousandths of an inch be left between the flange 20 and the upper end portion 2| of the bushing holder l2 so as to permit dust to enter and leave, because a narrower clearance frequently results in binding due to the entry of dust particles. The steel thrust washer 33 is easily renewed when worn and the entire device is easily maintained in accurate condition. Either set of the antifrictin bearing balls [3 or M takes the thrusts in the opposite direction, resulting from the insertion or withdrawal respectively of the rotary tool.

What we claim is:

1. A pilot device for guiding a rotary tool into a work piece comprising a bushing holder having a bore therethrough, a guide bushing structure rotatably mounted in said bore and having a tool-guiding bore therethrough co-axial with said bushing holder bore, said bushing holder having a pair of axially-spaced annular shoulders thereon, said bushing structure having a pair of axially-spaced annular shoulders disposed adjacent said bushing holder shoulders and in opposed spaced relationship therewith to form annular bearing recesses, and a spaced pair of annular anti-friction bearing element assemblies mounted in said bearing recesses, said bushin structure includin an annular bearing retainer mounted thereon adjacent one of said recesses.

2. A pilot device for guiding a rotary tool into a work piece comprising a bushing holder having a bore therethrough, a guide bushing structure rotatably mounted in said bore and having a tool-guiding bore therethrough co-axial with said bushin holder bore, said bushing holder having a pair of axially-spaced annular shoulders thereon, said bushing structure having a pair of axially-spaced annular shoulders disposed adjacent said bushing holder shoulders and in opposed spaced relationship therewith to form annular bearing recesses, a spaced pair of annular anti-friction bearing element assemblies mounted in said bearing recesses, said bushing structure including an annular bearing retainer mounted thereon adjacent one of said recesses, and an annular thrust member mounted on said bushing structure between said retainer and one of said assemblies.

3. A pilot device for guiding a rotary tool into a work piece comprising a bushing holder having a bore therethrough, a guide bushing structure rotatably mounted in said bore and having a tool-guiding bore therethrough co-axial with said bushing holder bore, said bushing holder having a pair of axially-spaced annular shoulders thereon, said bushing structure having a pair of axially-spaced annular shoulders disposed adjacent said bushing holder shoulders and in opposed spaced relationship therewith to form annular bearing recesses, and a spaced pair of annular anti-friction bearin element assemblies mounted in said bearing recesses, said bushing structure including an annular bearing retainer mounted thereon adjacent one of said recesses, said bushing holder having an outwardly extending flange at one end thereof remote from said retainer.

JAMES B. GIERN. ANDERS P. ANHOLTI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,353,295 Day July 11, 1944 FOREIGN PATENTS Number Country Date 361,981 Germany 1922 

